The present invention relates to a consumable cored wire comprising an optical fiber surrounded by a cover for measuring a temperature of a molten steel bath. The present invention also refers to a method and a device for producing the cored wire.
JP H0815040 (A) describes a method that feeds a consumable optical fiber into liquid metal for measuring the temperature of molten metal baths. A similar method and apparatus for optical fiber measurements of molten metals is also described in U.S. Pat. No. 5,730,527. Consumable optical fibers of this kind are known, for example, from JP H11160155 (A). These are single metal jacketed optical fibers where the optical core is covered by a metal covering, typically stainless steel, that serves the purpose to stiffen the optical fiber such that it can be immersed into molten metal. Whereas these immersible optical fibers can penetrate beneath the molten surface, they suffer from a rapid deterioration. Improvements to these early consumable optical fibers comprise additional protection structures and are known, for example, from JP H10176954 (A). Here, the optical fiber is surrounded by a protective metal tube surrounded by a layer of plastic material. The covered optical fiber immersed into the molten metal is fed from a coil or spool at a predetermined rate that would expose the tip of the optical fiber to the metal when deeply immersed. The depth of immersion at the time of exposure is important for temperature accuracy. Therefore, preventing early destruction or moving the optical fiber tip to the measuring point quickly are necessary for accurate temperatures.
JPH09304185 (A) discloses a feeding rate solution where the speed of fiber consumption must be greater than the rate of devitrification, thereby assuring that a fresh optical fiber surface is always available. It has been found that the availability of a fresh fiber surface is essential for an accurate temperature measurement and this availability depends upon how the fiber is immersed into the molten metal. Multiple feeding schemes are likely to arise due to the numerous variety of conditions to which the fiber will be exposed during its introduction into and through various metallurgical vessels at various times during metals processing. When variation in the rate of devitrification can be minimized by improvement in the consumable optical fiber construction, the applicability of the technique can apply to a wider range of metallurgical vessels without customization of the feeding regime.
Multi-layered wire structures with a steel outer covering are used in steelworks to introduce doping substances selectively into the molten steel bath. These are typically called cored wires and are described in DE 19916235A1, DE 3712619A1, DE 19623194C1 and U.S. Pat. No. 6,770,366. U.S. Pat. No. 7,906,747 discloses a cored wire comprising a material which pyrolizes upon contact with a liquid metal bath. This technology applies to the introduction of generally uniform powdered substances into a molten bath and lacks teaching of how to make, manufacture and introduce a cored wire with an optical fiber into molten metal.
U.S. Pat. No. 7,748,896 discloses an improved optical fiber device for measuring a parameter of a molten bath. The device comprises an optical fiber, a cover laterally surrounding the optical fiber, and a detector connected to the optical fiber, wherein the cover surrounds the optical fiber in a plurality of layers. One layer comprises a metal tube and an intermediate layer arranged beneath the metal tube. The intermediate layer comprises a powder or a fibrous or granular material, wherein the material of the intermediate layer surrounds the fiber in a plurality of pieces. The intermediate layer is formed of silicon dioxide powder or aluminium oxide powder and may contain a gas producing material. The disclosed feature of the intermediate layer surrounding the fiber in a plurality of separate parts means, in the sense of the invention, that the construction in multiple parts exists in the operating state; in other words, during or after immersion in the molten bath to be measured such that the pieces of the intermediate layer remain separate and are separable during use.
The layered structure aids in keeping the optical fiber at a very low temperature for a relatively long time. Devitrification from elevated temperatures that will destroy the optical fiber is delayed. From a particular temperature onwards during immersion into molten metal, expansion of the gases of the intermediate layer forcibly remove the un-attached cover layers. The fiber is heated erratically to the equilibrium temperature in the molten metal bath, so that the measurement can then take place very quickly before the optical fiber or its end immersed in the molten metal bath is devitrified.
U.S. Pat. No. 4,759,487 and U.S. Pat. No. 5,380,977 discloses a method of producing a type of optical cored wire where an outer stainless steel jacket intimately surrounds the optical fiber. This type of cored optical fiber, known as armored optical fiber, lacks an intermediate layer insulation layer, and thus the use of this optical cored wire is limited and the method of production is unsuitable for the present invention.
An objective of the invention is to further improve a cored wire for measuring the temperature of a molten bath, and in particular molten steel.